1. Field of the Invention
The present invention relates to a multistage amplifier constituted by field effect transistors (FETs) connected to each other in multiple stages. The transistors are monolithically formed around a central VIA hole. Predetermined electrodes of the various transistors are electrically connected to each other in the area immediately surrounding the central VIA hole.
2. Description of Related Art
A wiring pattern of a conventional multistage FET amplifier on a semiconductor substrate is shown in FIG. 5 (Prior Art). This is the pattern that is revealed in FIG. 7 of the paper entitled "X-Band Monolithic Four-Stage LNA with Pulse-doped GaAs MESFETs" in the document "GaAs IC Symposium Tech. Digest, 1990."
This prior art multistage FET amplifier is a four-stage amplifier in which four FETs 1 through 4 are connected to each other in four stages. Each of the FETs 1 through 4 is provided with a source electrode S, a drain electrode D, and a gate electrode G. The four FETs are monolithically formed on one semiconductor substrate. A lengthy wiring pattern is repeated in the prior art, as shown in FIG. 5 (Prior Art), between each FET, so that a multistage connection is formed from the first stage FET 1 through the final stage FET 4.
A second conventional construction of a multistage FET amplifier is an arrangement of a plurality of FETs in a single integrated circuit (IC) package with external FET interconnection wiring. A third arrangement exists in which a plurality of FETs, formed independently of each other in separate IC packages, are utilized and externally wired to constitute a multistage FET amplifier.
Each of the conventional multistage FET amplifiers revealed by prior art has problems. The multistage FET amplifier monolithically formed on a semiconductor substrate, as shown in FIG. 5, is relatively large in size. The size of the multistage amplifier is directly linked to the area occupied by wiring patterns and the number of VIA holes used. Each of the FETs 1 through 4 has two wiring patterns connected to its source electrode S and each of these wiring patterns is connected to a separate and distinct VIA hole H. Accordingly, the area occupied with the wiring patterns on the semiconductor substrate is large and the number of VIA holes required is great. This has an adverse effect on the size of the multistage amplifier and on the manufacturing yield.
The conventional multistage FET amplifier that comprises a plurality of FETs contained in a single IC package and external FET interconnection wiring also has problems. The external wiring that is required for this multistage amplifier considerably adds to its size and decreases the manufacturer's efficiency.
A conventional multistage FET amplifier constituted by using a plurality of FETs in independent IC packages is larger than a monolithically formed multistage FET amplifier. These multistage amplifiers have an additional problem. Scattering is introduced into the multistage amplifier because the characteristics of the FETs are different, as they were manufactured independently. Accordingly, the characteristics of such a multistage amplifier are unstable.